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## Main Question or Discussion Point

An element of the domain of a real-valued function of a real variable is often called a point. For example, an element (point) ##p## in the domain of a real-valued function ##f## of a real variable where ##f'(p)=0## or ##f'(p)## is undefined is called a critical point of the function. The particular type of critical point ##x## where ##f'(x)=0## is called a stationary point. As another example, "the graph ##y=(x+2)(x-1)^2## cross the x-axis at the points ##x=-2## and ##x=1##." In those cases, why we called a real number as a point? Is it because we view the real numbers as points in the context of the real line?